1. Field of the Invention
The present invention relates to an endoscope system, a processor device, and a method for operating an endoscope system, for enhancing structure of blood vessels and the like by use of narrowband light in observation.
2. Description Related to the Prior Art
In a medical field, diagnosis and treatment using an endoscope system, having a light source device, an endoscope, and a processor device, become widespread. For such diagnosis and treatment, normal observation and narrowband light observation are performed. In the normal observation, an observation object is imaged in its entirety by using broadband light such as white light. In the narrowband light observation, the structure of tissue such as blood vessels or ductal structure in the observation object is enhanced by using narrowband light having a specific narrow wavelength range.
In the narrowband light observation, both superficial blood vessels distributed in superficial tissue of the observation object and middle-layer blood vessels distributed in middle-to-deep tissue of the observation object are enhanced using blue narrowband light. However, there may be cases where the observation is focused only on the superficial blood vessels or the middle-layer blood vessels, depending on a purpose of diagnosis. In this case, it is desirable to enhance only one of the superficial blood vessel and the middle-layer blood vessel and suppress the other. According to U. S. Patent Application Publication No. 2012/0197076 (corresponding to Japanese Patent Laid-Open Publication No. 2012-152459), the superficial blood vessel or the middle-layer blood vessel is extracted from a B/G image, which has a luminance ratio B/G between a blue image having tissue information about the superficial tissue and a green image having tissue information about the middle-to-deep tissue. An image of the extracted blood vessel is superimposed on a base image, so that the superficial blood vessel and the middle-layer blood vessel are enhanced or suppressed selectively.
Of the blood vessels in the observation object, the superficial blood vessels are critical to the diagnosis. For the purpose of improving accuracy in diagnosis, it is desirable to display a superficial blood vessel, which is located deeper than a most superficial blood vessel, and the most superficial blood vessel, which is located in close vicinity to the surface of mucous membrane, in a distinguishable manner, and selectively enhance or suppress the blood vessels. However, in most cases, the blue image contains both of the most superficial blood vessel and the superficial blood vessel. It is difficult to extract the most superficial blood vessel and the superficial blood vessel independently from the B/G image described in the U.S. Patent Application Publication No. 2012/0197076, and hence to display the most superficial blood vessel and the superficial blood vessel separately or in a distinguishable manner.